1. Field of the Invention
This invention relates to a biocompatible ventricular assist and arrhythmia control device, and more particularly to a biocompatible ventricular assist and arrhythmia control device comprising a cardiac ventricular compression band-stay-pad assembly, for compressing and assisting in the contraction and expansion of one or both heart ventricles, without damaging the ventricle.
2. Description of the Prior Art
U.S. Pat. No. 4,925,443, issued May 15, 1990, to Marlin S. Heilman and Steve A. Kolenik, entitled "Biocompatible Ventricular Assist and Arrhythmia Control Device", discloses an implantable ventricular assist device which includes (1) one or more movable compression assemblies for engaging a ventricle of the heart; (2) an operating mechanism for cyclically actuating the movable compression assemblies and thereby alternately ejecting blood from the ventricle and permitting the ventricle to refill; (3) a sensing means to detect adequacy of ventricular stroke volume and/or pressure; (4) a control mechanism to assure adequate ventricular stroke volume by regulating the compressive force of the compression assemblies, and also to control pacemaker, cardioverter/defibrillator, and recorder subsystems; and (5) an electrical power source.
In that patent, each compression assembly includes a contoured pressure plate and a soft contact pad mounted on the interior plate surface for suturing and/or gluing the compression assembly to the ventricle. To minimize mechanical stress on the myocardial surface, including the coronary arteries, the contact pad consists of an elastomer, such as silicone rubber, or a thermoplastic material (Shore A durometer range 30-50). To avoid edge stress, the thickness of each contact pad is progressively reduced toward its periphery. To further reduce stresses on the myocardium, bearings and axles are used to mount the pressure plates on the compression assembly's driving arm; if the contracting heart produces a torquing force, the joint will permit the pressure plate, within specified limits, to follow the natural movement of the heart.
Similarly, to help prevent the edges of the compression assembly pressure plates from creating pressure points which might cause possible damage to the heart, a related continuation-in-part U.S. patent application Ser. No. 07/019,701, filed May 14, 1990, in the names of Marlin S. Heilman, et al., entitled "Biocompatible Ventricular Assist and Arrhythmia Control Device Including Cardiac Compression Pad and Compression Pad Assembly", now U.S. Pat. No. 5,098,369, discloses replacing the contact pad of each compression assembly with a gel-filled contact pad of special construction which compresses the heart ventricle more uniformly without damaging the ventricle.
Other previous attempts to provide ventricular assistance have ranged from artificial hearts (e.g., the Jarvik-7), to devices which directly pump the blood via an artificial pathway inserted through the ventricular wall, to devices which exert pressure on the outside of the heart. Most frequently, these latter pressure-exerting devices involve some form of flexible bladder within a support structure such that expansion of the bladder presses on the ventricle and facilitates expulsion of blood. See, for example, U.S. Pat. Nos. 3,233,607 to Bolie; 3,279,464 to Kline; 3,587,567 to Schiff; 3,371,662 to Heid et al.; 4,048,990 to Goetz; 4,192,293 to Asrican; 3,455,298 to Anstadt; 4,690,134 to Snyder; 4,731,076 to Noon et al.; and 4,957,477 to Lundback. Another structurally related device (U.S. Pat. No. 4,506,658 to Casile) envisions a truncated conical structure of sac-lined rigid panels separated by contractible and expandable sections, and another device (U.S. Pat. No. 4,621,617 to Sharma), which is electromagnetically controlled, comprises a pair of hinged compression members. Further, U.S. Pat. No. 4,536,893 to Parravicini envisions using two segmented sacs, selectively fed by a pumping fluid to compress the right and left ventricles separately.
In general, bladder systems usually have various shortcomings. These include the possibility of catastrophic bladder fluid leakage (as a result of the fluid pressures involved), a propensity for damaging the heart surface due to poor fixation and/or rubbing of the bladder against the heart's surface, and the unnatural convex form presented to the heart's surface during systolic bladder expansion.
Another type of cardiac assist system is designed to compress all or part of the heart by alternately tightening and releasing a compression band. For example, one proposed system for body organs (U.S. Pat. No. 4,304,225 to Freeman), such as the heart, involves a flexible strap which is fixed to a contoured plastic block and passes across the back of the heart. In response to electrical pulses, a motor assembly alternately reels in and releases the flexible strap, thereby tending to flatten and force fluid from the heart.
The above-mentioned Freeman patent also discloses the use of a tubular compression sleeve which substantially encircles the heart and which comprises a series of interconnected expandable elliptical chambers. In use, a liquid solution is pumped into the sleeve from a supply chamber, causing the elliptical chambers to expand radially inward to compress the heart in its systolic phase. The solution then is released from the sleeve back to a supply chamber, permitting the heart to expand in its diastolic phase.
U.S. Pat. No. 4,583,523 to Kleinke and Freeman illustrates a heart assist mechanism which compresses the aorta, rather than a ventricle, and it compresses during the diastolic phase of cardiac contraction instead of the systolic phase. Other known prior art of interest includes U.S. Pat. Nos. 3,668,708 to Tindal, 4,167,046 to Portner, 4,092,742 to Kantrowitz et al. and 4,291,707 to Heilman, German Patent Document No. DE-A-2,557,475, British Patent Document No. GB-A-2,060,174 and U.S.S.R. Patent Document No. SU-1572646-A1.